Microwave process and apparatus



Nov. 14, 1967 H. c. ANDERSON 3,352,704

MICROWAVE PROCESS AND APPARATUS Original Filed April 10, 1961 FIGAINVENTOR HAROLD C. ANDERSON ATTORNEY 3,352,704 MICROWAVE PROCESS ANDAPPARATUS Harold C. Anderson, Rockville, Md., assignor to LittonSystems, Inc., Silver Spring, Md.

Original application Apr. 10, 1961, Ser. No. 101,741, now Patent No.3,281,856, dated Oct. 25, 1966. Divided and this application July 2,1964, Ser. N 0. 380,014

7 Claims. (Cl. 117-36.8)

ABSTRACT OF THE DISCLOSURE A spin resonant recording medium formicrowaves characterized by changing the physical shape or configurationof its surface in response to absorbed energy.

This invention generally relates to the recording of radiant microwaveradio beams by spin resonance technology and is particularly concernedwith the recording medium for recording of the beam in the form ofdeformed images or patterns over the surface of heat sensitive plasticmaterials. This is a division of pending application Ser. No. 101,741filed Apr. 10, 1961, now Patent No. 3,281,856.

In an earlier application of the same assignee, Ser. No. 59,342, filedSept. 29, 1960, now Patent No. 3,238,511, there is disclosed processesfor directly recording a radiant microwave intelligence beam in the formof detectable images on a tape or other record member by employing spinresonance technology. In the processes disclosed, the microwave beam isrecorded by presensitizing a spin resonance material into absorptiverelation with the frequencies of the beam whereby the energy beingabsorbed varies the characteristics of the material or its surroundingsin such manner as to produce a reproduceable pattern of the beamcharacteristics. In another prior application, Ser. No. 118,407, filedJune 20, 1961, now Patent No. 3,158,678, there is disclosed otherrecording processes wherein the radiant microwave beam is recorded inthe form of a visible color density image by employing the energyabsorbed from the beam to vary the color characteristics of certainchemical or physical materials,

According to the present invention, there is provided a recording mediumfor permitting the direct recording of radiant microwave beams inpermanent or semi-pen manent physical image form that differ from thoseof the prior applications by providing a recording in the form of aphysical deformation pattern of the beam over the surface of certainplastic materials. Very generally, the recording medium employedaccording to the invention includes a means, such as a layer of spinresonant material, for directly converting the energy of the radiantbeam into a spatially dispersed heat pattern image of the intelligenceand a second means, such as a layer of thermoplastic material in heattransferring relationship with the first layer, that responds to theheat image to provide a pattern of ripples, indentations, or otherphysical changes in the surface of the material according to theintelligence characteristics of the microwave beam.

In one preferred embodiment of the invention, the heat pattern beingobtained from the spin resonance absorption phenomena is applieddirectly to the surface of a heat sensitive thermoplastic material toraise the temperature of the material to above its critical temperature.This heating of the plastic maerial in the desired surface patterndirectly produces a change in the state of the material to vary thesurface finish of the material and capture and record the heat image inpermanent or semi-permanent form. According to a second preferredembodiment of the invention, the heat image is applied to athermoplastic material to produce a heat softened pattern over the sur-United States Patent face thereof, and by means of additional steps, thethermoplastic material is also uniformly stressed by means such as anelectrostatic field. As a result, only the heat softened areas over thesurface of the material are distorted or deformed by the stressing forceto provide a very pronounced pattern or physical image corresponding tothe heat image, whereas those areas over the surface that have not beenheated remain undisturbed and in their original surface configuration.

It is accordingly a principal object of the invention to provide arecording medium for directly converting a time variable radiantmicrowave intelligence beam into a deformed surface image of the beam ona thermoplastic material.

A further object is to provide such a recording medium for converting abroad frequency band of such microwave beams into frequency spectrumimages in permanent or semi-permanent form.

A still further object is to provide such a recording medium employingspin resonance materials.

Still another object is to provide such a recording medium wherein thesignal is recorded as embossed or deformed surface patterns along athermoplastic record member.

A still further object of the invention is to provide improved recordingtapes or record means for radiant microwave beam recording.

Other objects and many additional advantages will be more readilyunderstood by those skilled in the art after a detailed consideration ofthe following specification, taken with the accompanying drawings,wherein:

FIG. 1 is a perspective view generally illustrating one preferredrecording tape and the manner of applying a magnetic field in a radiobeam to effect the recording thereof,

FIG. 2 is a perspective view of the tape of FIG. 1 and furtherillustrating the nonuniform magnet means for enabling spectral imagerecording on the tape,

FIG. 3 is a perspective view illustrating a second embodiment of theinvention, and

FIG. 4 is a sectional view taken lengthwise along the tape in FIG. 3.

Referring now to the drawings, for a detailed consideration of oneprefer-red embodiment of the invention, there is generally illustratedin FIGS. 1 and 2, a preferred recording tape construction 10 togetherwith recording means for directly converting a time variable microwavebeam 18 into a physically deformed surface pattern or embossing alongthelength and width of the tape or other record member 10.

As is generally shown, the tape or record member is comprised of a basesupporting layer 11 of Mylar or other suitable base material, eitherrigid or flexible, over the surface of which is provided a coating orimpregnation of a spin resonance material 12, containing a considerablenumber of free or uncoupled electrons, or other subatomic particlestherein. A third or upper layer 13 on the tape is preferably comprisedof a coating or impregnation of a thermoplastic material, such as a wax,or other suitable thermoplastic that is characterized by providinga-physical change in its surface condition upon being subjected to atemperature exceeding its critical temperature, as will be discussedmore fully hereafter. The recording tape 10 is heated and maintained ata temperature just under its critical temperature by a regulatedexternal heating source generally indicated as 19.

A frame or region on the record member to receive a recording of themicrowave beam is subjected to a high intensity static magnetic field15, as indicated by the arrow lines numbered 15, by such means as beingintrov duced between the opposing poles 16 and 17 of a permanent magnetor electromag-net of suitable strength. This static magnetic field 15uniformly orients the magnetic dipoles in the spin resonance materialand serves to tune these dipoles into energy absorptive relationshipwith a radiant electromagnetic beam 18 in the manner of a resonantcircuit to absorb energy from the'beam.

For recording the microwavebeam, the magnetically tuned region or frameof the tape is then directly exposed to a polarized beam 18 of themicrowave signal, Which beam 18 may be introduced by a waveguide or thelike (not shown) and'directed to uniformly illuminate the frame orregion on the tape. The polarization of the microwave beam 18 iscontrolled suchthat its H component is made transverse to that of thestatic magnetic field to exert a reaction torque on the dipoles in theresonant material layer 12. Upon exposure to the microwave beam 18, theresonant material 12 in the region or frame exposed to the beam absorbsenergy from the beam and reradiates this energy in the ten h of heatthereby to raise the temperature of the absorbing resonant material 12.

Thus in the manner described, the microwave energy is absorbed andconverted by the resonant layer 12 into a spatial heat pattern acrossthe tape 10 in the region or frame exposed to the beam. This heatpattern, being in contact with the upper layer 13 of thermoplasticmaterial, is therefore applied to the thermoplastic layer in the samepattern configuration thereby serving to raise the temperature ofdiscrete positions over the thermoplastic surface above the criticaltemperature thereof.

For converting this heat pattern into a permanent or semi-permanentsurface image on the plastic, the plastic material layer 13 may, in onepreferred form thereof, be of a material having a relatively low heat offusion and having a relatively narrow or critical temperature range atwhich the material changes from a solid to a plastic or liquid form.According to the invention, a material having these characteristics isprovided with a dull or roughened upper surface finish 14 as isgenerally indicated in FIG. 2, which may be obtained by serrating,scraping, or otherwise roughening the upper surface of the layer 13.Upon the application of the heat pattern thereto, the temperature ofthose different positions or areas over the surface 14 receiving theheat image are raised above the critical temperature to melt or fuse thematerial at those discrete positions whereas vthe remaining surfaceareas of the plastic layer 13 are not sufiiciently heated to thiscondition. This fusing of the material renders the upper surface of theplastic smooth and glassy at those heated areas, as is generallyindicated in FIG. 1 at 40, thereby providing the upper surface of thetape with an alternate surface configuration of smooth and dull orroughened areas over the plastic layer 13 corresponding to the patternof the heat image applied thereto. After cooling of the heated areas onthe tape, this image pat-. tern over the surface of the plastic isretained or frozen by the rehardening of the plastic thereby to providea deformed surface configuration corresponding to the pattern of themicrowave beam 18. 7

One thermoplastic material providing the characteristics desired forpracticing the invention is a wax composition material sold by theTempil Corporation of New York, N.Y., under the name Tempilag. Thismaterial is obtainable in liquid form and when applied as a thin coating13, it dries with a dull or frosty upper surface finish 14. Upon heatingthis wax to its critical temperature, the surface of the materialbecomes glassy and smooth in the regions heated, and upon cooling andrehardening thereof, it retains this smooth surface, clearly indicatingthe regions or areas that were previously heated. This wax material isalso desirable in possessing a relatively'low heat of fusion and inabruptly changing from a solid to a liquid or partially liquid statewithin a narrow criticaltemperature range. As discussed above, thesefeatures are desirable since the low hea of. fusion renders this plasticmaterial more sensitive to weaker heat patterns, and the abrupttemperature range of melting enables the rough-smooth surface pattern tobe obtained with greater definition. However, as generally indicatedabove, a wide variety of other thermoplastic materials may be employedin practicing the invention ineluding other waxes, both natural andsynthetic resins, and various ones of the gels.

Among the other known materials having narrow critical temperatureranges are phenyl salicylate, biphenyl, diphenyl, para-toluidine, andp-bromo aniline.

FIG. 2 generally illustrates the manner of obtaining the recorded imageas a dispersed frequency spectrum of the radiant beam 18. As shown, thiseffect is provided by supplying a nonuniform magnetic field 15transversely across the tape 10 by such means as providing magneticpoles 16 and 17 with progressively diverging pole faces disposed in adirection across the tape 10. At the right, where the pole faces arepositioned more closely to gether, the magnetic field being producedthrough the tape is at the strongest intensity, Whereasat the left wherethe pole faces are disposed furthest apart, the magnetic field beingproduced through the tape is at the weakest intensity. In the region inbetween, the magnetic field accordingly becomes progressively weakerfrom right to left, thereby to provide a uniformly varying field acrossthe tape having a different intensity at each transverse position.

As is described more fully in the 'c opendin'g applications discussedabove, the spin resonance materials can ployed in the layer orimpregnation 12 are frequency sensitive and absorb energy from theradiant beam 18. only at a frequency related to the intensity of thestatic magnetic field 15-to which they are subjected. In other words,such materials may be tuned by the magnetic field to respond todifferent frequencies. Accordingly, by providing a nonuniform magneticfield transversely across the tape, each different transverse positionon the tape is tuned to respond only to a different frequency in thebeam 18 and each position is effectively transparent to otherfrequencies. Thus, upon illuminating all positions in the frame with theradiant beam 18, each different frequency component in the beam 18 isabsorbed at a different transverse position across the tape to provide aspectral frequency image of the beam 18.

FIGS. 3 and 4 illustrate a second preferred embodiment and method ofpracticing the invention. In this embodiment, the recording tape 20 maybe essentially the same as in FIGS. 1 and 2 and comprise a base orsupport layer 21, an intermediate layer 22 of dispersed spin resonancematerial, and an upper thin layer 23 of a suitable wax or otherdeformable thermoplastic material, such as a silicone gel or the like.

The radiant microwave beam 18 may be convertedinto a spatial heatpattern image on the tape 20 in the same manner as described above bysubjecting a frame or image region on the tape to an intense magneticfield 15 to presensitize or tune the spin resonance layer 22 to thefrequencies to be recorded and simultaneously subjecting this tunedregion to the radiant microwave beam 18, being directed over a coaxialcable 25 and through a waveguide recording head 24 to uniformlyilluminate the complete frame. The heat image being obtained in theresonant layer 22 is applied directly to the upper plastic layer 23 toprovide a pattern of heat softened areas or positions on the tape 20corresponding to the radiant beam.

To develop this heat image into a deformed surface pattern according tothe second embodiment, the tape 20 is then removed from the radiant beamrecording zone and is positioned under a source of negatively chargedelectrons 26 where the upper surface of the plastic layer 213 isuniformly sprayed or wiped with electrical charges 31 as generallyindicated in FIG. 2. After receiving the layer of charges, the tape 20is next passed through a high intensity electrostatic direct currentfield, such as may be obtained from a flat plate 27 and a lowerrod 28positioned at opposite sides of the tape and energized by a high voltagedirect current source 29. The positive terminal of this field is locatedat the rod 28 below the tape thereby to exert a downward force on theelectrons 31 disposed over the upper surface of the tape. Where the tapehas been heat softened by the recording heat pattern, the downward forceexerted upon the electrons 31 by the electrostatic field succeeds inpushing aside or deforming the surfaces of the tape to provide a visiblepattern of indentations thereon as generally indicated at 32, whereasthose positions on the plastic layer that have not been heated andsoftened by the heat pattern resist the downward pull on the electrons31 to maintain their previous surface finish.

Thus, according to the second embodiment of the invention, the heatpattern being obtained from the radiant beam produces a pattern of heatsoftened positions in the plastic corresponding to the frequencies ofthe radiant beam 18 and the application of a uniform stress over thesurface of the material by means of the electrostatic field operates todistort or deform the surface regions that have been previously softenedto produce a very pronounced deformation pattern or physical image overthe surface of the plastic corresponding to the intelligence of themicrowave beam.

After the recording of the beam has been completed, the tape 20 is thencooled to solidify or freeze the deformed image pattern in the plasticthereby to provide a permanent or semi-permanent image as is desired.

In performing the steps of applying the uniform electric field to stressthe plastic layer 23 as described, it is preferred that the uppersurface of the plastic layer 23 first be sprayed or wiped with anegatively charged layer of electrons 31 from a suitable source 26, asdescribed, and that thereafter the plastic member be subjected to a highintensity transverse electric field by means of the capacitor plate 27and rod 28. However, the step of negatively charging the surface of theplastic is not essential to deforming the plastic layer 23 and theapplication of a sufficiently strong electric field being appliedbetween the plate 27 and the rod 28 or by a pair of plates will, byitself, deform the heat softened areas on the thermoplastic material 23in the manner described.

As generally indicated above, the cooling and consequent rehardening ofthe heat softened areas on the plastic layer 23 serves to freeze andpermanently retain the deformed pattern or image in the plastic.However, if it is desired to erase this pattern and restore the plasticlayer to its blank or undeformed condition, this may be easily performedby uniformly heating the entire recording member so that the plasticflows to fill in the cavities, undulations, wrinkles and the like 32,forming the deformed surface pattern. If desired, the further step ofcombing or leveling the upper surface of the flowable plastic layer 23may also be practiced to insure a uniform and level upper surface.Alternatively, a large number of thermoplastic materials are known thatpossess a plastic memory and will return to their original shape andconfiguration upon the application of heat. By using these knownmaterials, the embossed or deformed surface pattern may be erased byapplying sufiicient heat to the recording tape to enable the plasticlayer 23 to return to its original condition.

Although in the process steps as described above, the heat pattern isfirst applied to the plastic layer 23 and thereafter the electricalstressing force is uniformly applied to deform the heat softened areas,it is believed evident that these steps may be reversed in time. Byreversing the steps, the plastic layer 23 may be first subjected to auniform electric stressing field that is normally insufficient to deformthe hardened plastic but is sufiicient to deform the plastic after ithas been heat softened by the heat image. The result is, therefore, thesame since the plastic layer 23 will be deformed in the pattern of theheat image.

The intensity of the electric field and/or the magnitude of theelectrical charges 31 applied to the thermoplastic may also be varied asdesired, as may the thickness of the layer 23 of the thermoplasticmaterial being employed. With regard to the thermoplastic materials, awide variety of dielectric thermoplastics are suitable for thisembodiment such as various of the waxes, the natural and syntheticresins, and various gelatinous materials, such as those formed ofsilicone oil.

Briefly considering the phenomena of spin resonance and some preferredmaterials that may be employed in the spin resonance layer orimpregnation, it is known that in certain materials, such as in freeradical materials, and certain crystals, numerous uncoupled or unpairedparticles, such as electrons, may exist or be created. These unpairedparticles endlessly spin in orbits within the materials when subjectedto an external magnetic field and the rate of spin or spin speeds of theparticles are known to be controlled by and proportional to theintensity of the externally applied magnetic field. As a result of beingcharged electrical particles that are continuously moving or orbiting,these particles will respond to external radiant radio beams in themicrowave frequency. In responding to the radio 'beams, the orbitingparticles behave in the manner of a resonant circuit with the resonantfrequency at which they respond to absorb energy from the beam being afunction of the spin rate of the particles which, in turn, is controlledby the intensity of the external magnetic field to which the particlesare subjected. The energy being absorbed by the orbiting particles isconverted into heat by essentially two methods. In the first, thespinning elec trons or other particles collide with surroundingparticles to give off heat, and this phenomena is termed spinlatticerelaxation effects. Secondly, the spinning particles emit energy in theform of electromagnetic waves which are received and absorbed by othermatter in the material. This latter effect is termed spin-spinrelaxation effects.

According to the present invention, the free radical materials arepreferred for use in the layer 12 of FIGS. 1 and 2 or 22 in FIGS. 3 and4 and one suitable material of this type which is obtainable in stableform is the material diphenylpicrylhydrazyl (DPPH). This material is afree radical material possessing numerous unpaired electrons and isstable at ambient temperatures. It is obtainable in small grain solidparticle form whereby layers, coatings, or impregnations thereof may beeasily applied to the Mylar or other base tape in the manner described.However, as discussed in much greater detail in the copendingapplications listed above, numerous other crystal materials, freeradical materials, and others possessing these characteristics may beemployed in practicing the invention.

Although but two preferred processes and apparatus have been illustratedand described, it is believed evident that many changes and variationsin the process steps and in the materials employed may be made withoutdeparting from the spirit and scope of this invention. Accordingly thlsinvention is to be considered as being limited only according to thefollowing claims appended hereto.

What is claimed is:

1. A recording member for providing a surface deformation pattern of amicrowave signal comprising a base member, a layer of spin resonancematerial supported by said base member and characterized by possessingnumerous unpaired subatomic charged particles therein, and a layer ofthermoplastic material combined with said base member and said spinresonant layer and in heat conducting relationship therewith, andcharacterized by responding to heat in the spin resonant layer toprovide a change in the physical shape of the surface of thethermoplastic material corresponding to the heated areas.

2. In the recording member of claim 1, said layer of spin resonancematerial comprising a free radical containing material.

3. In the recording member of claim 1, said thermoplastic material beingcharacterized by possessing a critical narrow range of temperature atwhich the material undergoes a change of state.

4. In the recording member of claim 3, said thermoplastic materialhaving an uneven surface finish whereby a temperature produced change ofstate therein varies the surface configuration of said material.

5. A recording member for radiant radio beams comprising a supportmeans, a layer of material containing free radicals supported by saidmeans, and a layer of dielectric thermoplastic material dispersedintimately with said free radical material on said support means andresponsive to a critical change in temperature to change the physicalshape of its surface in a deformation pattern indicating the heatedareas.

6. In the recording member of claim 5, said support means comprising abase layer, said freeradical material 8 I comprising an intermediatelayer supported on the base and thermoplastic material comprising anupper layer.

7. A process for forming a radiant radio beam recording membercomprising the steps of dispersing a mass of microwave spin resonantmaterial over an extended region of a base support and applyingthereover a liquid coating of thermoplastic material being characterizedby solidifying with a dull surface finish, possessing a low heat offusion, responding to a critical change of temperature to change from asolid to a liquid state, and re solidifying after such change of stateto a smooth surface finish.

References Cited UNITED STATES PATENTS 3/1966 Anderson 340-173 20TERRELL w. FEARS, Primary Examiner.

1. A RECORDING MEMBER FOR PROVIDING A SURFACE DEFORMATION PATTERN OF AMICROWAVE SIGNAL COMPRISING A BASE MEMBER, A LAYER OF SPIN RESONANCEMATERIAL SUPPORTED BY SAID BASE MEMBER AND CHARACTERIZED BY POSSESSINGNUMEROUS UNPAIRED SUBATOMIC CHARGED PARTICLES THEREIN, AND A LAYER OFTHERMOPLASTIC MATERIAL COMBINED WITH SAID BASE MEMBER AND SAID SPINRESONANT LAYER AND IN HEAT CONDUCTING RELATIONSHIP THEREWITH, ANDCHARACTERIZED BY RESPONDING TO HEAT IN THE SPIN RESONANT LAYER TOPROVIDE A CHANGE IN THE PHYSICAL SHAPE OF THE SURFACE OF THETHERMOPLASTIC MATERIAL CORRESPONDING TO THE HEATED AREAS.